Yale study finds that gun violence is a ‘contagious’ social epidemic

Gun violence is often described as an epidemic or a public health concern, due to its alarmingly high levels in certain populations in the United States. It most often occurs within socially and economically disadvantaged minority urban communities, where rates of gun violence far exceed the national average. A new Yale study has established a model to predict how “contagious” the epidemic really is.

Led by Andrew Papachristos, associate professor of sociology at Yale, the researchers analyzed a social network of individuals who were arrested during an 8-year period in Chicago, Illinois — a city that has rates of gun violence more than three times the national average. The team studied connections between people who were arrested together for the same offense, and found that more than 60% of all gun violence during this time period happened in “cascades” — or connected chains — through these particular social networks.

This image is a graphical representation of the largest connected component of the network. Each node represents a unique individual. Red nodes identify subjects of a fatal or nonfatal gunshot injury; blue nodes represent people who were not subjects of gun violence. Data are from the Chicago Police Department.

“We want to take this epidemic of gun violence out of the criminal justice paradigm and put it in a public health context that focuses on victims and the reduction of trauma,” says Papachristos, corresponding author on the study.

The study also determined that an individual within these social networks was at the greatest risk of being shot within a period of about 125 days after their “infector,” the person most responsible for exposing the subject to gun violence, was the subject of gun violence. These results provide evidence that gun violence is not just an epidemic, but it has specific network patterns that might provide plausible opportunities for interventions, notes Papachristos. “There is a real value in understanding the timing of these events as a way to identify victims, and where we can insert resources such as violence- and harm-reduction programs into these networks.”

“If we want to drop gun violence rates in this country, we have to care about the young men with criminal records who become victims of gun violence,” says Papachristos. “By and large these are young men of color who have criminal records. Their lives are worth saving.”

Other authors on the study included Ben Green ’14 and Thibaut Horel from Harvard University.